Well, it seems like the blogs in the last few days found the answer.
It has converted to a prepaid-only credit.

https://frequentmiler.com/citi-aadva...paid-bookings/

For cardholders existing prior to July 15, you can use it as usual through the end of 2025.
Starting 2026, and starting immediately for all cardholders applying after July 15, you can only use the credit on prepaid bookings.